CSS (Cascading Style Sheets) is a stylesheet language used to describe the presentation of a document written in HTML or XML. CSS saves lots of work as formatting elements only need to be applied to one CSS file rather than individually formatting every HTML page. CSS rules consist of selectors that point to the HTML element to style paired with a declaration block containing CSS properties and values to determine how that element will look. Common CSS properties include those to control text formatting, background effects, borders, lists, links and positioning.